A modern wireless communication system, such as Code Division Multiple Address (CDMA), Wideband Code Division Multiple Address (WCDMA), Universal Mobile Telecommunication System (UMTS), Long Term Evolution (LTE), is a variable envelope modulation technology which sufficiently utilizes frequency spectrum and simultaneously adopts amplitude modulation and phase modulation. The technology has a higher Peak-to-Average Power Ratio (PAPR) and a wider dynamic range, while an excessively high PAPR causes a transmitting end to impose a very high requirement on linearity of a power amplifier and usually to run below an envelope peak level.
The variable envelope modulation technology needs to use a linear power amplifier to amplify a signal, which is realized generally by adopting an Envelope Tracking (ET) based technology in order to guarantee a linearity and increase a power amplification efficiency. As shown in FIG. 1, a radio frequency signal is input, then is driven and amplified by a driving amplifier, and is output to a radio frequency power amplifier. Meanwhile, an envelope detector retrieves an envelope waveform signal of the radio frequency signal, the envelope signal is amplified through a fast tracking power supply, and the amplified envelope signal is used as radio frequency power amplifier drain voltage; and finally the amplified radio frequency signal is output by the radio frequency power amplifier.
With the development of multi-carrier technology, when the fast tracking power supply is linearly amplifying the retrieved envelope signal, a higher requirement is imposed on a bandwidth and an efficiency of the fast tracking power supply. For example, in the procedure of performing envelope amplification, a bandwidth of the envelope signal can be up to dozens of MHz, it is very difficult for a bandwidth of an ordinary switch power supply to satisfy a requirement of an ET bandwidth due to limitation of such factors as a semiconductor technology and a switch frequency. Furthermore, output noise and distortion are modulated to a carrier, which results in out-of-band spectrum spreading and seriously influences an Adjacent Channel Power Ratio (ACPR) of the signal. Hence, a new high efficiency and high bandwidth fast tracking power supply is required to adapt to continuously developing application demands.